Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 251915 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 315 PM EDT Sun Sep 25 2016 .SYNOPSIS...
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A frontal boundary will remain stalled to our south tonight while high pressure passes to our north. The high will move off the coast Monday. A cold front will pass through the area overnight Monday into Tuesday. An upper-level low will likely impact the area during the middle portion of next week.
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&& .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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As of early this afternoon...a stationary front was sitting to our south in the Carolinas with high pressure over southeastern Canada. Easterly flow has promoted cloud development across southern parts of the CWA...particularly west-central Virginia where the flow is bumping up the Blue Ridge. Further north, the high`s influence has been more apparent with drier air and sunnier skies. Tonight, a cold front currently in the Mississippi Valley will push eastward and the high will shift east as well. THis will cause the flow to gradually become more southeasterly and increase moisture flow into the region. Low clouds will become more widespread after diminishing for a time this afternoon and a little drizzle or perhaps a shower may occur in west-central Virginia. Further north and east it should stay less cloudy and radiational cooling should allow temps to drop down into the 50s and even some 40s.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
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Cold front will cross the region from west to east during the period followed by potential cyclogenesis at the end of the period as a strong upper low drops southeastward towards the area. Monday morning will start fairly cloudy especially towards the southwest (west-central VA) where upslope flow will be ongoing. Some drizzle or showers will be possible here. As we head through the day, the front will approach and clouds at higher levels will become more widespread as well. Think highs manage the low 70s before the clouds get too dense to block the sun completely but its not impossible most places get stuck in the 60s. Showers will start to push east from the west as we head through the afternoon but thunder odds are not high given we stay fairly stable on the north side of the front over the Carolinas. Main fgen band with front moves through Monday night. It may slow down as it crosses the area in response to the upper low dropping down from the Great Lakes but think it should generally clear the CWA by later Tuesday. Instability will be minimal since warm sector will have trouble coming back north ahead of the cold front (which really will likely pass our area as more of an occluded front) but forcing aloft with high PW`s may be enough to squeeze out some thunder. Rainfall amounts very uncertain but a decent rain on the order of a half inch is expected...perhaps more if the forcing is strong enough and the front slows down enough. Lows will stay relatively mild with the clouds and rain Monday night...50s and 60s...while temps should try to rebound into the 70s on Tuesday after clouds break. Things get very uncertain as we head into Wednesday. Tuesday night should start out dry but as the upper low approaches from the west cyclogenesis may begin in our area by midday Wednesday which would result in the redevelopment of showers. Still lots of uncertainty here so have kept highs in the 70s...but if the more pessimistic scenarios happen we may be stuck in the 60s Wednesday.+
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
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A cutoff upper level low over the Great Lakes will push south and east towards our area Wednesday night and into Thursday... and possibly Friday. There is uncertainty on the exact details of the forecast as guidance is in disagreement with location timing of the upper level low. If it pushes further south, a coastal low pressure could develop over the Mid-Atlantic region. With this scenario the chance of showers over our CWA extends from Wednesday night and into Friday, and dry conditions into the weekend. If the upper level low lingers to our west and north then the chance of showers could extend from Wednesday night into the weekend. Basically, expect a chance of showers Wednesday night into Friday and uncertain into the weekend... depending on position of the upper level low.
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&& .AVIATION /19Z SUNDAY THROUGH FRIDAY/...
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Low clouds have been persistent around CHO today and may linger through tonight into Monday. Further north VFR continues and should stay that way through tonight into Monday before the front approaches. However, the low clouds near CHO may encroach northward late tonight so MVFR cigs are not impossible...especially at IAD and MRB. Sub-VFR and quite possibly IFR cigs/vis expected Monday night as front moves through with rain. Improving conditions by Tuesday afternoon then perhaps worsening again later Wednesday as another storm approaches. Sub-VFR conditions possible Wednesday night and maybe into Saturday as upper level disturbance could bring showers into the region. Details with this forecast are uncertain as guidance is in disagreement at this moment.
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&& .MARINE...
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Light winds tonight with high pressure, then SCA takes effect midday tomorrow through tomorrow night with front approaching and then crossing area with rain. May need to extend into Tuesday depending on winds behind front. SCA may again develop Wednesday as another system approaches. Small craft advisory possible Wednesday night and into Friday as coastal low could develop off of the Mid-Atlantic coast. Winds could be diminishing into Saturday but it is uncertain at the moment.
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&& .TIDES/COASTAL FLOODING...
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Despite NEly flow, a surge in water has been noted across the MD portion of the Chesapeake Bay and the Tidal Potomac. Water levels have remained below minor coastal flood thresholds on this lesser high tide (except it was met at Straits Pt this morning). Washington DC SW Waterfront has their high tide at 4:30pm this afternoon and the water level will be very close to the minor threshold of 4.2ft. The high tide this evening/overnight is the greater of the two today and weakening NEly flow this evening should aide positive anomalies to persist. Coastal flooding is expected tonight at least at Annapolis and the DC SW Waterfront and possible at Straits Pt, Solomons Island, and Baltimore. Onshore flow will increase and turn to the southeast for Monday through Monday night. Minor flooding is likely during this time...especially during the high tide cycle Monday night which will be the higher of the two astronomical norms. Should the SEly winds be a little stronger, a coastal flood watch may be necessary for Monday night.
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&& .CLIMATE... Unusually warm weather has persisted over the area for quite some time. Autumn-like temperatures are finally making an appearance over the area, and DCA has finally fallen below 60 degrees this morning for the first time since June 9th (total of 107 days). The record most consecutive days at or above 60 degrees in the Washington DC area is 112 set in 2012. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from noon Monday to 6 AM EDT Tuesday for ANZ530>543. && $$ SYNOPSIS...RCM NEAR TERM...RCM SHORT TERM...RCM LONG TERM...IMR AVIATION...IMR/RCM MARINE...IMR/RCM TIDES/COASTAL FLOODING...BAJ CLIMATE...LWX

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